This invention relates generally to sleep recording. More particularly, it relates to sleep recording without body surface sensors.
Standard sleep recording or polysomnography is typically performed in a sleep laboratory using ten to twenty body-surface sensors (electrodes, elastic bands, etc.) to record various medically significant features of sleep such as electrocardiogram and respiratory movements or efforts at thorax and abdomen. The attachment of sensors using glue and tape and the routing of wires along the skin typically requires ninety minutes or more and is performed by a trained polysomnographic technician. The social context of the pre-sleep period is substantially modified and the subsequent sleeping conditions are widely acknowledged to be aberrant. Ambulatory versions of the above methodology using portable battery-powered recorders allow traditional sleep recording to be performed at a subject""s home. A night of ambulatory polysomnography requires the same amount of technician time (in addition to travel time) as does sleep laboratory recording, and incurs the same discomforts associated with body-surface sensors. Though ambulatory polysomnography takes place in the home, the social context of the pre-sleep period is again modified by the extended personal interaction with the polysomnographic technician.
A number of U.S. Patents describe apparatus combined and/or integrated with mattresses in order to recognize a patient""s activity during his/her sleep period.
U.S. Pat. No. 4,320,766, for example, describes a capacitive motion sensor layer placed under a mattress or the like for monitoring the movements of a person. The sensor layer is uniformly placed over the sleep area in order to recognize the person""s motion, respiratory movements and heart beat during sleep. The sensor layer provides a single signal stream. Hence, the invention provides only a limited ability to derive motion information of individual body parts by filtering signal patterns from the single recorded signal. In addition, the system is only able to recognize motion and not various types of sleeping position, like for example, a stretched out or an embryonic sleeping position. In addition, the device is not suitable to make distinct measurements from abdominal and/or thorax movements.
U.S. Pat. No. 5,435,317 discloses a device for detecting a respiratory dysfunction of a person located in a bed, cot, crib or the like and for inducing a rocking motion. Four peripheral transducers are placed in a cross-like fashion within a framework designed to carry a mattress and to recognize a persons movements. The apparatus is configured to count movements rather than interpreting the nature and source of the movements. The cross like arrangement of the transducers corresponds to a mechanical movement amplification mechanism and to provide observation of the whole mattress area. The transducer positions are not defined to recognize particular body movements. The crude design of the apparatus is not suitable for a qualitative observation of sleep motion.
U.S. Pat. No. 5,611,096 discloses an apparatus for adjusting the pressures of a therapeutic mattress surface in accordance with the angular position of that surface. The apparatus comprises an angular position sensor and a rotation sensor, which are housed together in an enclosure mounted on the mattress top or the adjustable portion of the mattress supporting frame structure. The angular position sensor and the rotation sensor are configured and positioned for providing feed back of the angular mattress orientation defined by the supporting frame structure. The angular position sensor and rotation sensor are not configured to respond to a patient""s movements or position.
U.S. Pat. Nos. 5,684,460 and 5,796,340 describe fluid filled sensing pads or cavities extending across a sleeping area of a mattress and being connected to transducers. The apparatus is also configured to count movements rather than interpreting the nature and source of the movements. The recognition of individual localized movements, for example, of thorax and abdominal region are limited. In addition, the volume of the sensing pad has a certain flexibility, that alters pressure information derived especially from low frequency and high amplitude impulses as they result for instance from breathing movements.
U.S. Pat. No. 5,844,488 discloses a sensor pad for installation on top and across the width of a mattress proximate the midsection of a reclining patient. The sensor pad is configured to recognize a patients movement toward an edge of the bed. The configuration includes central and edge switching areas. Hence, the sensor pad is solely able to recognize if or if not a patient is within an area defined by the switching areas"" extensions. The sensor pad is not able to make qualitative interpretation of the patient""s sleeping location or sleeping behavior.
U.S. Pat. No. 5,846,206 describes a method for observing the wakefulness of a vehicles driver by utilizing pressure sensor plates being in contact with the person to recognize heart beat and respiration of it. The pressure sensor plates are configured to recognize pressure related information. The patent does not disclose particular positioning or configuration of the pressure sensitive plates. Moreover, the method is mainly designed for a continuous threshold observation rather than a qualitative recording of the vehicle driver.
U.S. Pat. No. 5,914,660 describes the use of gravity switches for consistent infant observation against Sudden Infant Death Syndrome. The patent does not describe how the gravity switches are implemented or configured.
U.S. Pat. No. 5,989,193 describes the use of a pressure area sensor placed in a mattress below a patient. The sensor provides only a single signal stream with all limitations described above. In addition, the placement of the sensor beneath the mattress reduces the recording sensibility significantly, since the mattress has a major damping effect especially on high frequency and low amplitude movements like, for example, heart beat.
Finally, U.S. Pat. No. 6,011,477 describes a respiration and movement monitoring system having a mattress surface sensor and an optional accelerometer sensor attached to a mattress support platform. The mattress surface sensor has a spiral configuration and evenly covers a central sleeping area. The surface sensor recognizes respiratory movements. The uniform coverage of the sleeping area with the single surface sensor restricts the system to a movement counting rather than interpreting the nature and source of the movements. The level of recognition is limited to trigger preventive action against Sudden Infant Death Syndrome but not suitable for polysomnography.
None of the inventions described above provide the signal bandwidth necessary to retrieve sleep information compatible with clinical systems. Therefore, there exists a need for a cost effective monitoring apparatus that can be utilized for continuous sleep behavior monitoring and that does not impair a persons natural sleep or pre sleep behavior. The invention described in the following addresses this need.
A mattress device for monitoring sleep behavior is introduced that may be configured as a commercially available product or be placed as an additional mattress device on top of a commercial mattress. The mattress device provides sleeping comfort compatible to that of conventional mattresses and encourages a patient to monitor his/her sleep behavior on a continuous basis. In the preferred embodiment, three monitoring regions are defined to capture relevant sleep behavior information. The monitoring regions are an abdominal region, a thorax region and a leg region. Sensors are positioned and configured in correspondence with a mattress core layer and a mattress top layer to independently recognize dynamic leg, abdominal and thorax movements with a broad signal bandwidth to capture movements ranging from heart beat or voice activity to myoclonic movements of individual body parts. In addition, the sensors respond to angular deformations of the mattress top layer induced by the patients weight.
In the preferred embodiment, the sensors are DC accelerometer sensors that have a dynamic response to motion and a static response dependent on their angular position. The dynamic response characteristic recognizes movements of a mattress core layer and a mattress top layer induced, for example, by a patient""s breathing, heart beat, snoring, abdominal activity, thorax movements, limb movements and voice. The sensors are configured in conjunction with the mattress core layer for low frequency and high amplitude sensitivity across the corresponding sensing area. Low frequency and high amplitude movements may be induced on the mattress core layer, for example, by a patient""s respiratory movements. The sensors are configured in conjunction with the mattress top layer for high frequency and low amplitude sensitivity across the corresponding sensing area. High frequency and low amplitude movement may be induced on the mattress top layer, for example, by a patient""s heartbeat, leg movements, or voice. The mattress top layer responds similar to a membrane and may be tuned by adjusting a tensile preload of it.
The angular position of the sensors depend on the distance at which the corresponding body region imprints the mattress structure.
The sensors"" response to dynamic movements and static position result in two dimensional signals of each sensor. Hence, by using three sensors, a six dimensional signal space is provided that provides information versatility at a level that is compatible with a clinical sleep behavior monitoring. Yet, the invention is simple and can be cost effective fabricated, which makes the monitoring and interpretation of sleep behavior possible for individuals on an ongoing base.
The signals derived from the sensors are collected using a data acquisition unit, which are then converted to numbers, monitored, and stored, all in a continuous fashion preserving clock time. The data acquisition unit can be a laboratory-standard software hosted in a workstation or can be specialized hardware and/or software now available for a laptop computer or any other computing device suitable of managing the data amount provided by the mattress device. An alternative is to use a signal multiplexor and a laptop equipped with a sound card. On-line or off-line digital signals analysis routines, such as bandpass filtering, but also including more advanced signal separation methods are applied to the accelerometer signals outputs to separate the components deriving from cardiac activity, respiration, body, and limb movement, body position etc. Affordable computers provide sufficient capacity to process, interpret and present the generated data amount at the time the invention was made. Standard computer features like, for example, sound processing capabilities may be utilized to process the sensor signals which may be recoded in order to have a frequency spectrum compatible to that conventionally managed by a commercial sound cards.